Semiconductor devices in which external wiring is wire-bonded onto a surface electrode are known. With a semiconductor device of this type, stress is applied to the surface electrode when the external wiring is wire-bonded onto the surface electrode. The stress applied to the surface electrode is transferred to a contact region formed in an area exposing at a surface of a semiconductor substrate and may damage the contact region. Damage to the contact region inhibits carrier flow and causes device performance of the semiconductor device to deteriorate.
In a semiconductor device disclosed in Patent Document 1, an interlayer insulating film is provided on a surface of a semiconductor substrate between adjacent contact regions. A surface electrode that is in contact with the contact regions is formed on the surface of the semiconductor substrate. A nickel layer is formed on an entire surface of the surface electrode. External wiring is wire-bonded to a surface of the nickel layer. The surface electrode is formed of aluminum and is softer than the nickel layer. Therefore, when the external wiring is wire-bonded to the surface of the nickel layer, stress applied to the nickel layer during wire bonding is absorbed by the surface electrode and stress transferred to the contact regions is relaxed.    Patent Document 1: Japanese Patent Application Publication No. 2008-28079